This invention relates in general to integrated circuit packaging, and more particularly to improved integrated circuit packages for enhanced automated visual detection of downbond sites during wire bonding.
High performance integrated circuit (IC) packages are well known in the art. These high-performance IC packages include, for example, plastic chip carrier packages, leadless plastic chip carrier packages, quad flat pack IC packages, and others.
In order to provide uniform ground and power supplies to IC packages and to reduce electrical noise, it is desirable to have many ground bond interconnects. Commonly, IC packages include many ground wires to the die attach pad of the leadframe, which is traditionally flooded with silver for ease of manufacture.
Downbond wire length affects the tuning of the IC circuit, particularly in high frequency operations. As a result, IC packages commonly employ a leadframe that has a number of electrically conductive contacts, a die attach pad and a conductive ring or rings, conductive lines or an array of conductive dots formed generally around the circumference of the die attach pad and between the die attach pad and the contacts. Typically, the ring(s), lines or dots of the array are used as power and/or ground planes and are formed of silver stripes or dots on the bare copper leadframe. A semiconductor die is mounted on the die attach pad and electrically conductive bond wires are used for electrical connections between bond pads on the semiconductor die and the leads, the die attach pad and the ring(s) or dots of the array. The silver on the copper leadframe is detectable by an automated vision system for a robotic wire bonding apparatus. Thus, the silver dot, stripe or ring on the copper leadframe are identified for wire bonding to an accurate and repeatable position.
Unfortunately, the copper leadframe is subjected to thermal processes such as die attach curing and wire bond heating that cause the copper to oxidize from a brown copper color to blue, or in some cases to a silver color. This often occurs when a problem is encountered during the wire bond process. For example, if operator assistance is required, the leadframe strip often sits on a high temperature heater block until the operator arrives, by which time the copper has turned silver in color. This is particularly problematic as the vision system of the wire bonding apparatus uses the silver rings, lines or dots on the copper background in order to accurately and repeatably wire bond. The vision system, however, may not be able to differentiate between the silver rings, lines or dots and the oxidized copper background. Thus, the wire bonding apparatus fails to bond or bonds in the wrong location.
Accordingly, it is an object of an aspect of the present invention to provide a leadframe having characteristics for improved downbond registration during automatic wire bonding.
According to an aspect of the present invention, there is provided a process for enhancing visual detectability of a copper leadframe having a die attach pad and a plurality of contacts, during automated wirebonding in the production of an integrated circuit package. The process Includes selectively plating silver on the die attach pad of the leadframe and around a periphery of the die attach pad and surface treating the leadframe to cause a color change on a surface of the leadframe for improved visual detectability of the selectively plated silver.
According to another aspect of the present invention, there is provided a leadframe having a die attach pad for mounting a semiconductor die thereon, a plurality of conductive leads circumscribing the die attach pad, silver plating disposed on a portion of the die attach pad, around a periphery thereof and a layer of organo-metallic complexes on at least a portion of the die attach pad and the contact pads.
According to another aspect of the present invention there is provided an integrated circuit package. The integrated circuit package includes a die attach pad, a semiconductor die mounted to a portion of the die attach pad, at least one row of conductive leads circumscribing the die attach pad, silver plating disposed on a portion of the die attach pad, around a periphery of the die attach pad and outside a perimeter of the semiconductor die, and a layer of organo-metallic complexes on at least a portion of the die attach pad and the contact pads.
According to yet another aspect of the present invention, there is provided the use of a mixture of at least one triazole compound with a polymeric stabilizer to cause a color change on a surface of a copper leadframe for improved visual detectability of selectively plated silver.
According to still another aspect of the present invention, there is provided the use of a mixture of hydrogen peroxide and benzotriazole to cause a color change on a surface of a copper leadframe for improved visual detectability of selectively plated silver.
Advantageously, the chemical dipping of the copper leadframe ensures that there is a visually discernable difference between the copper and selectively plated silver. Thus, the silver can be easily identified by a visual detection system for automated downbonding (wirebonding). In one embodiment of the present invention, the chemical dipping does not degrade the wire bondability performance of the silver plated surfaces. In one embodiment of the present invention, the chemical dipping improves adhesion of the mold compound to the copper surface.